Study On Deformation Law Of Deep Foundation Pit In Subway Station With Silty Clay Layer

During the construction of urban subways,the research on the deformation law of deep foundation pits for subway stations under different geological conditions is a very important issue in geotechnical engineering.It can provide reference and guidance for the design and construction of similar projects.It has a strong practical significance.This paper takes the deep foundation pit project of Shiguang Street Station of the first phase of the No.1 line of Shijiazhuang Rail Transit as the research background.Based on the theoretical analysis and on-site monitoring,the three-dimensional numerical simulation of the excavation process of the foundation pit based on FLAC3 D software is carried out.The deformation regularity and its influencing factors of deep foundation pits in metro station in silty clay layer are discussed and analyzed.The main work and conclusions are as follows:(1)Through reviewing a large number of related literature,the deformation mechanism and its influencing factors of deep foundation pits are summarized and analyzed.It is concluded that the deformation of deep foundation pit during the excavation process mainly includes the deformation of the envelope structure and the uplift of the bottom of the foundation pit.The settlement of the ground surface outside the pit;the main factors affecting the deformation of the deep pit are intrinsic factors,design factors and construction factors.(2)By monitoring the monitoring data and analyzing the monitoring results,it is concluded that the horizontal displacement of the deep foundation pit retaining structure in the silty clay layer gradually increases with the increasing depth of excavation,and the position where the maximum horizontal displacement occurs gradually moves downward.The distribution of the deformation curve is in the shape of “parabola”;the distribution pattern of ground settlement around the pit is gradually changed from “triangle” to “groove”;the erection of steel supports effectively limits the deformation of deep foundation pits.The monitoring results indicate that the design of the deep foundation pit envelope structure and the formulation and implementation of the monitoring plan are both reasonable and effective,ensuring the safety and stability of the foundation pit during the construction process.(3)Through the use of FLAC3 D software,a three-dimensional numerical simulation of the excavation process of the foundation pit was carried out to compare the calculation results and monitoring results of the horizontal displacement of the retaining structure,the ground settlement outside the pit and the axial force of the steel support under four conditions.Outgoing: There are some deviations in numerical values between the numerical simulation results and the field measurement results,but the deformation laws of the foundation pits are basically the same.The feasibility of this model for simulating the excavation of foundation pits is preliminary verified.(4)By using FLAC3 D software,starting from the intrinsic factors and design factors,the influencing factors of deep pit excavation in silty clay layer were discussed and analyzed.It was concluded that in the inherent factors,the elastic modulus of the soil was adjusted.The values of the internal friction angle and cohesion force will cause the horizontal displacement of the envelope structure,the ground surface settlement outside the pit and the axial force of the steel support to be changed to some extent,but the overall distribution law of the deformation remains unchanged;design factors in a certain range,the horizontal displacement value of the envelope structure and the ground surface settlement value outside the pit can be effectively reduced by appropriately increasing the pile diameter and the depth of the embedded pile of the retaining pile and increasing the rigidity of the steel support.After the stability of the pit reaches a certain level,the contribution of these parameters to the stability of the pit begins to become smaller.In addition,the horizontal spacing and vertical position allocation of steel supports also have a certain influence on the deformation of deep foundation pits.In the design and construction process,the distribution form of steel supports must be reasonably set.